The aim of the proposed research is to determine how the Nucleus of the Optic Tract (NOT) contributes to production of optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN) and to habituation and suppression of the vestibulo-ocular reflex (VOR) in the monkey. Previous studies indicate that NOT processes information that activates the velocity storage mechanism in the vestibular system to produce the slow component of OKN and OKAN. Concurrently, it produces rapid inactivation of a "dump" of activity for contralateral OKAN and vestibular nystagmus from velocity storage. It also mediates a signal that supports habituation of vestibular nystagmus or OKAN with contralateral slow phases. In the next grant period we will inject GABA agonists and antagonists into NOT and determine the effects on OKN, OKAN and the VOR. We will make lesions of NOT and investigate the time course of return of visual suppression and habituation of contralateral vestibular nystagmus. We will study if visual suppression, habituation, VOR gain adaptation, and ocular pursuit are affected by such lesions. We will record from identified neurons in NOT and OKAN with visual suppression of vestibular nystagmus. These experiments should determine how NOT and the visual system participate in the production of OKN, OKAN and in controlling the VOR through visual suppression. They should also be useful in determining which brainstem and cerebellar organizations are involved in stabilizing gaze and mediating habituation of the VOR.